.mask{
    width:100%;
    height:100%;
    background: rgba(0,0,0,0.2);
    position: fixed;
    top:0;
    left:0;
}
form{
    width:500px;
    height:300px;
    position: absolute;
    left:50%;
    top:50%;
    margin-left:-250px;
    margin-top:-150px;
    background: #fff;
}
p{
    margin:5px;
    background: #fff;
}
table,td,th{
    border: 1px solid #ccc;
}
.error{
    color: #f66;
}